ARTIFICIAL FLIGHT. 545 



machine it is necessary to tilt the aeroplane more nearly 

 vertical, after the manner of a bird coming to rest. We 

 want to check the horizontal speed as much as possible, 

 accordingly the drift must be as great as possible, and here 

 the concav^e surface is again the best. 



Although most practicable designs for flying machines 

 involve the use of the screw as a means of propulsion, Mr. 

 Hargrave has constructed models working with flapping 

 wings and finds little difference between the efficiency of 

 this means of propulsion and a screw. But even here fixed 

 aeroplanes were used in addition, and there can be little 

 doubt that the ultimate form of the flying machine will be 

 one supported on fixed planes driven through the air at high 

 speeds. Several fanciful schemes for constructing gigantic 

 air ships propelled by other means have been put on paper 

 and have even lately appeared in print, but these must be 

 viewed with suspicion. It remains to add ^ that Professor 

 Langley and Mr. Maxim with small slanting planes have 

 been able to support about 250 pounds per horse-power, 

 exerted, and the latter, by using heavier weights, about 133 

 pounds per horse-power. Both of. these figures, taken in 

 •conjunction with previous results, show that, so far as 

 purely mechanical difficulties are concerned, the problem of 

 flight is soluble. 



(iii.) Balance and stability. — If it is of fundamental im- 

 portance that a ship should be properly balanced and should 

 not be liable to overturn, the same applies with even greater 

 force to an aerial machine ; but the conditions to be satisfied 

 in the latter are more difficult of investigation, and failure in 

 this respect is attended with greater and more certain disas- 

 ters in mid-air than on water. In his lecture to the British 

 Association at Liverpool last year. Dr. Elgar pointed out 

 that the stability of ships was not investigated mathemati- 

 cally till after many vessels had sunk, and that our present 

 knowledge was only acquired as the result of considerable 

 sacrifice of human life. The sad ending which befel Herr 

 Lilienthal just when his experiments were beginning to be 

 attended with their greatest success is the most unfortunate 

 ^British Association Nottingham Report, p. 872. 



